An enclosed high-voltage switchgear having phase-segregated poles and an electromagnetic noise measuring system is described, for example, in the article "Operation and Diagnosis Assisting System for Substations," Hitachi Review, vol. 40, no. 5 (1991) pages 359-366. In the measuring system described in this article, a spectral analysis technique is performed on the detected noise signal in order to obtain more information about the nature of the noise inside the enclosed high-voltage switchgear. This type of measuring system, however, presents many sources of error, and the probability of an error occurring increases with the number of sensors.
European Patent A 342,597 describes a measuring system for enclosed high-voltage switchgear, in which various sensors, some of which are the same as each other and some of which are not, detect partial discharge processes, the measured values of which are analyzed with regard to the intensity and duration of their occurrence. When a large enough difference exists between two measured values that are under comparison with each other, it is concluded that there is a fault in the system. Such a large difference can also occur when only a single measured value is recorded, in which case a second value is therefore assumed to be equal to zero. This could also occur if two measured values are recorded by different sensors with a great time difference. Superfluous error messages could possibly be generated in this way.
The article entitled "Proceedings of 1991 IEEE Power Engineering Society, Transmission and Distribution Conference," pages 467-472 (1991), states that irregularities in electric lengths between the sensors and the processing device can be compensated in differential measurements on high-voltage switchgear.